The production of hydrocarbons and oxygenated hydrocarbon derivatives from synthesis gas (i.e., carbon monoxide/hydrogen) is a developing technology, and it is increasingly being introduced into commercial applications. Reaction conditions for synthesis gas conversion generally involve temperatures in the range of about 150-500.degree. C, pressures in the range of about 15-10,000 psi, carbon monoxide/hydrogen molar ratios in the range of about 10:1 to 1:10, and hydrogenation catalysts selected from Group VIII metals.
The technical literature on synthesis gas conversion is extensive. Illustrative of prior art publications are U.S. Pat. Nos. 2,681,924; 2,686,195; 2,686,801; 2,696,506; 2,729,664; 2,753,367; 2,767,202; 2,770,635; 2,786,863; 2,957,902; and the references cited therein.
Efforts to convert synthesis gas into a definitive class of products has not been readily accomplished. Most synthesis gas conversion processes yield a broad molecular weight distribution of products, which range from methane to polymeric derivatives.
In German Offen. No. 2,503,233 there is a detailed review of prior art literature relating to the use of rhodium metal as a synthesis gas conversion catalyst. Selective production of oxygenated two-carbon hydrocarbons from synthesis gas is a desirable objective, but prior art processes report only low yields of products such as acetic acid, ethanol, acetaldehyde and ethyl acetate.
German Offen. No. 2,503,233 describes an improved process for converted synthesis gas into oxygenated C.sub.2 -hydrocarbon derivatives in the presence of a rhodium metal catalyst. The preferred catalyst is 5% rhodium metal on a silica support.
There remains a need for improvements in catalysts and processes for efficient and highly selective conversion of synthesis gas into oxygenated C.sub.2 -hydrocarbon products.
Accordingly, it is an object of the present invention to provide a process for selective conversion of synthesis gas into oxygenated C.sub.2 -hydrocarbon products such as acetic acid, ethanol, acetaldehyde and ethyl acetate.
It is another object of this invention to provide an improved process for converting synthesis gas into acetic acid with an efficiency of at least about 30 weight percent.
It is another object of this invention to provide an improved rhodium catalyst which is highly reactive and highly selective for conversion of synthesis gas into oxygenated C.sub.2 -hydrocarbon products.
It is a further object of this invention to provide a method for preparing and pretreating a hydrogenation catalyst adapted for selective conversion of synthesis gas into acetic acid.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.